The present invention is directed, in general, to materials manufacturing and, more specifically, to a method of determining a crystallographic quality of a material located on a substrate.
The advance of the technology of multilevel metal oxide semiconductor (MOS) devices has evolved immensely as the MOS industry strives for faster and more reliable MOS devices. Currently, there is a drive to transition from well-established aluminum metallization, tungsten interconnects, and titanium and titanium nitride barrier layers to copper and its associated materials. For the process of multilevel metallization, the crystallographic nature of the metallization and the nucleation of grain size and structure will have an increasing effect on the quality and yield of the products that are produced. Typically, aluminum deposits via chemical vapor deposition along a well-established fiber texture defined by its {111} plane of atoms. In contrast, copper and the new barrier materials do not have the same baseline orientation as does the aluminum, and therefore might have orientation problems, and more importantly, electromigration (EM) problems that arise from the abnormal grain orientations. As a result, there is a need to be able to accurately discern grain morphology and orientation, such that high quality MOS devices may be manufactured.
Electron Backscatter Kikuchi Diffraction (BKD) has become a viable way to discern both the grain size, crystallographic orientation, and phase determination of materials common to the processing of semiconductors. The Electron Backscatter Kikuchi Diffraction method analyzes collections of backscattering Kikuchi diffraction patterns, therefore, it combines the advantages of point orientation in transmission electron microscope (TEM) with morphological information over a large enough area to provide statistical relevance. The Electron Backscattering Kikuchi Diffraction method has gained wide acceptance, because the broad information about the structure at an atomic crystallographic level cannot easily be discerned by the other techniques commonly known in the art.
However, the Electron Backscatter Kikuchi Diffraction method has problems. One of such problems, is the Electron Backscatter Kikuchi Diffraction method""s inability to accurately discern between two adjacent grain structures which are misaligned with a rotation angle of greater than about five degrees. When the grain size of the material being subjected to the Electron Backscatter Kikuchi Diffraction method is on the same order as the spread of the backscattered electron intensity reflection by the incident electron beam and the size of the interaction volume of the diffraction contains a grain boundary, overlapping patterns are generally more discernable. For the transition from well-established aluminum metallization, tungsten interconnects, and titanium and titanium nitride barrier layers, this poses a real problem. Of the barrier layers, titanium nitride, titanium, cobalt silicide, tantalum nitride and others have grain structures that are approaching the size of the area of backscattered electron intensity. For copper interconnects, sigma three twinning creates the same effective change in lattice orientation, thereby creating a misidentification with the boundaries and twin boundaries. These misidentifications then prevent the Electron Backscatter Kikuchi Diffraction method from accurately detecting smaller off axis grain nucleations out of the boundary structure, from the misidentification of overlapping grain structures.
Currently, a ranking scheme is conducted to approximate which grain orientation solution is detected most often for overlapping grain boundaries. The solution that is detected the most times is then determined to be the correct solution. The problem with the ranking scheme is that it does not always provide the correct solution of the grain orientation. For example, it is common for the solution of the grain orientation to be inconsistent with the grain orientations available in the material being tested. Furthermore, the ranking scheme uses a finite number of test plots, which may provide room for statistical error.
Accordingly, what is needed in the art is a method of determining a crystallographic quality of a material located on a substrate, even though overlapping crystallographic patterns may be present, that does not experience the inaccuracies present in the prior art methods.
To address the above-discussed deficiencies of the prior art, the present invention provides a method of determining a crystallographic quality of a material located on a substrate. The method includes determining a set of crystallographic solutions for an unknown crystallographic orientation, and subsequently comparing the set of crystallographic solutions to adjacent known crystallographic orientations, to determine the unknown crystallographic orientation. In a preferred embodiment, the set of crystallographic solutions may be a rank of crystallographic solutions which may represent the most probable crystallographic orientations. The rank of crystallographic solutions, in an alternative embodiment, may be represented by a vote, a fit and a confidence index.
The above disclosed method, in contrast to prior art methods, is substantially able to accurately determine the crystallographic orientation of two overlapping Kikuchi band formation patterns. Since the set of crystallographic solutions is carried forward until two adjacent known crystallographic orientations have been determined, a more accurate determination of the unknown crystallographic orientation may be found.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.